This invention relates to the manufacture of abrasive tools. More specifically, it relates to making tools with abrasive grains disposed in discrete parcels separated from neighboring parcels on the cutting surface by open channels. The invention further relates to self-sharpening abrasive tools in which the abrasive parcels are formed from multiple, ultrafine abrasive grains embedded therein.
In certain abrasive tools for industrial applications abrasive grains are affixed to a metal preform. The grains are attached to the preform by brazing a metal bonding composition at temperatures above about 600xc2x0 C.
Removing swarf from the cutting zone during grinding improves performance. Among other things, swarf removal reduces wear of the brazed bonding composition and premature dulling of the abrasive grains. Cooling the work piece is another way abrasive tool users obtain improved grinding performance. Often cooling is accomplished by bathing the work piece in a cool, liquid lubricant. By providing open spaces on the abrasive tool, manufacturers can enhance swarf removal and cooling efficiency. These open spaces provide paths for swarf to leave the cutting zone and conduct coolant to and from the work piece.
A typical method of creating swarf removal and coolant spaces involves cutting grooves or drilling holes through the preform. This technique is widely used in abrasive wheel manufacture. In segmented abrasive tool fabrication, channels can be created by placing gaps between abrasive segments. Normally, such segments are molded from mixtures of abrasive grains and bonding composition and then attached as units to the tool. These methods add to the complexity of the manufacturing operation, are time consuming, and add to product cost.
It is desirable to provide an efficient method of making an abrasive tool with swarf removal and cooling space. Some methods for placing abrasive grains in discrete locations separated by open space on an abrasive tool have been suggested.
U.S. Pat. No. 5,389,119 (Ferronato et al.) discloses a method of making a nonwoven fabric with discrete islands of abrasive bound to a porous fabric layer. The islands are created by masking portions of a conductive fabric layer and electro-depositing or electroplating a metal structure which contains abrasive material in isolated, unmasked spots.
U.S. Pat. No. 4,826,508 (Schwartz et al.) teaches a method of forming a flexible abrasive member which includes applying a flexible mask of non-electrically conductive material having a multitude of discrete openings therein to one side of a flexible fabric, placing the fabric with the mask applied in a metal deposition bath, and depositing metal directly in the discrete openings in the presence of particulate abrasive material such that the metal adheres directly to the fabric and the abrasive material becomes embedded in the metal deposits.
U.S. Pat. No. 4,047,902 (Wiand) discloses a method of manufacturing a metal-plated abrasive product which entails providing a conductive or metallic backing member, masking off predetermined desired surface portions thereof to leave exposed, spaced-apart portions on the backing, and bonding abrasive grit particles to the exposed portions. The bonding is carried out by a metal plating process.
U.S. Pat. No. 4,863,573 (Moore et al.) teaches a method of making an abrasive article by screen printing a non-conductive mesh with non-electrically conductive ink. The mesh is passed through an electroplating bath while in contact with an electrically conductive cylinder or metal band. A first, nearly complete thickness of metal is electrodeposited onto the non-printed areas of the mesh. Then abrasive particles are deposited on the metal and a second, outer layer of metal is electrodeposited onto the first thickness of metal. The abrasive particles thus are captured by the outer layer of metal and lie at the surface of the metal.
U.S. Pat. No. 4,874,478 (Ishak et al.) provides a method of making an abrasive member comprising attaching a metal film to one surface of a flexible sheet, applying a mask of plating resistant material having a multitude of discrete openings to the exposed surface of the film and depositing metal directly through the openings into the metal film in the presence of particulate abrasive so that the metal adheres to the film and embeds the abrasive in the metal deposits.
Each of the foregoing references relates to manufacture of flexible abrasive fabric or film. Although these abrasive articles might be laminated to supporting substrates to form coated abrasive products, they generally cannot be used by themselves in many industrial grinding applications. Fabric or film-borne abrasive tools will not hold up in aggressive grinding of construction materials, such as steel and concrete. Additionally, each referenced method employs electro-deposition or electroplating to attach the abrasive to the fabric. Such methods of attachment do not usually provide sufficient thickness of bond material to endure in demanding, industrial grinding applications.
Other approaches to incorporating open space in an abrasive matrix have been disclosed. U.S. Pat. No. 4,882,878 (Benner) describes a grinding wheel having a rigid, continuous abrasive-bearing matrix. The matrix has a plurality of spaced apertures extending into the wheel from the grinding surface. Preferably the matrix is of an organic binding material.
International Patent Application WO 96/26811 (Ferronato) discloses a flexible abrasive member having a backing layer on one side and deposits of abrasive particles and bonding material on the other side. The article further includes a permanent one way mold substantially encircling the deposits and extending along at least part of the height of the deposits. The deposits are placed in holes of the flexible abrasive member.
U.S. Pat. No. 5,152,917 (Pieper et al.) teaches the method of making a structured, coated abrasive article comprising a backing bearing a plurality of abrasive composites having precise shape and disposed in a non-random array. The method includes introducing a slurry of binder precursor and abrasive grains into cavities on the outer surface of a production tool. A backing is placed over the outer surface such that the slurry wets one major surface of the backing to form an intermediate article. The binder precursor is then cured before the intermediate article departs from the outer surface of the production tool. The binder precursor is a quick setting, curable or thermoplastic organic resin.
The prior art does not satisfy the need for a metal preform abrasive tool for aggressive grinding applications in which discretely spaced apart abrasive elements are strongly attached to the preform with a brazeable metal bonding composition. Accordingly, there is provided a process for making an abrasive tool comprising the steps of:
(A) providing a stencil having a plurality of perforations of selected shape;
(B) contacting a cutting surface on the abrasive tool with the stencil whereby the perforations define cavities adjacent the cutting surface;
(C) providing a brazing paste including a metal braze composition and a binder component;
(D) filling the cavities with brazing paste;
(E) removing the stencil to form parcels of brazing paste on the cutting surface, each parcel being separated from neighboring parcels by paste-free channels;
(F) depositing abrasive grains onto the parcels; and
(G) thermally processing the abrasive tool to braze the abrasive grains to the cutting surface.
In another aspect, the present invention provides a process for making a metal preform abrasive tool in which selectively shaped and spaced apart parcels of brazing paste are first formed on a transfer medium. The brazing paste parcels are then transferred to the cutting surface of a metal preform where abrasive grains are added and brazing is accomplished. This method facilitates the manufacture of oddly-shaped and curved cutting surface abrasive tools. There is thus provided a process for making an abrasive tool comprising the steps of:
(A) providing a stencil having a plurality of perforations of selected shape;
(B) contacting a transfer medium with the stencil whereby the perforations define cavities adjacent the transfer medium;
(C) providing a brazing paste including a braze composition and a binder component;
(D) filling the cavities with brazing paste;
(E) removing the stencil to form a patterned face of parcels of brazing paste on the transfer medium, each parcel being separated from neighboring parcels by paste-free channels;
(F) forcing the patterned face against a cutting surface of the abrasive tool;
(G) peeling the transfer medium away to leave the parcels on the cutting surface;
(H) depositing abrasive grains onto the parcels; and
(I) thermally processing the abrasive tool to braze the abrasive grains to the cutting surface.